One of the things I like about a long-running blog is that I can revisit long-running stories whenever I feel like it. And one of the longest of those stories has been unfolding in a lab at Michigan State University since 1988. That year, a biologist named Richard Lenski began rearing Escherichia coli from a single microbe. The bacteria, which he raised in a dozen separate flasks, all faced the same challenge: endure a starvation diet that their lab-pampered ancestors had not suffered.

Every few hours, the bacteria reproduced. Each morning, the scientists took a few drops from each flask and moved these colonists to a fresh flask. Mutations arose, which the descendants inherited. Some helped the bacteria grow faster than